Influence of Salinity on Micronutrient Availability in Soil and Plant in Cowpea-Groundnut Cropping System

An experiment on cowpea-groundnut rotation was conducted to study the effect of saline irrigation water on the availability of micronutrient cations (Fe, Zn, Cu and Mn) in soil and in plants with the effect of a gradual imposition of irrigation salinity (ECiw). Three saline treatments (S1: 2.0 dS m-1, S2: 4.0 dS m-1, S3: 6.0 dS m-1 with a control S0) were maintained in long-term field trials. In summer (cowpea) the soil ECe was raised to 6.01 dS m-1 while in kharif (groundnut) the ECe was 2.21 with S3. A noticeable increase in soil pH (from S0 to S3) was also observed in cowpea (0.48 unit) and groundnut (0.97 unit) seasons. The four available micronutrients in soil did not show any significant trend in both seasons. The concentration of both shoot Fe and Zn increased from control (S0) to highest salinity (S3) to the tune of 19% and 74% respectively in groundnut. The accumulation of root Fe and Zn in groundnut declined to the tune of 53% and 40% respectively with the increasing salinity from S0 to S3. For cowpea, only Zn content showed a decreasing trend among the other micronutrients. Genotypic variation of groundnut did not affect the accumulation of micronutrients as observed by testing eight groundnut genotypes in the present study. A significant drop in yield was noticed for both crops due to saline irrigation, and the groundnut yield varied between 1.6 t ha-1 (in S0) to 0.14 t ha-1 (in S3). This study marks a relevance where very less information is available on micronutrient availability in plant tissues and soil under changing salinity, especially for groundnut, which is considered an important oilseed crop from the national perspective.